Conventionally, air conditioners are known as refrigeration apparatus in which a plurality of indoor units are connected in parallel with one another through refrigerant piping with respect to a single outdoor unit in order to form multi-type indoor units, as disclosed in the Japanese Patent Application Laid Open Gazette No. 4-208370. The outdoor unit has a compressor, a four-way selector valve, an outdoor heat exchanger, an outdoor motor-operated expansion valve and a receiver. The indoor unit has an indoor motor-operated expansion valve and an indoor heat exchanger.
In a cooling operation, a refrigerant discharged from the compressor is circulated, so as to be condensed at the outdoor heat exchanger, reduced in pressure at the indoor motor-operated expansion valve, evaporated at the indoor heat exchanger and then returned to the compressor. In a heating operation, a refrigerant discharged from the compressor is circulated, so as to be condensed at the indoor heat exchanger, reduced in pressure at the outdoor motor-operated expansion valve, evaporated at the outdoor heat exchanger and then returned to the compressor.
Further, in the outdoor unit, the capacity of the compressor is regulated according to the load of the indoor unit.
In the above-mentioned air conditioner, since only a single outdoor unit is provided, many kinds of outdoor units are required having different capacities from one another to correspond with the indoor load, i.e., the number of indoor units to be connected. In addition, when the indoor load does not correspond with the capacity of the outdoor unit, the capacity of the outdoor unit is disadvantageously increased in spite of a small indoor load.
To cope with the above problems, a plurality of outdoor units, for example, two outdoor units, having different capacities from one another, may be combined with one another in order to form multi-type outdoor units.
In such a case, when the outdoor unit under cooling or heating operation and the outdoor unit in deactivation exist at the same time, the refrigerant must be prevented from being stored in the outdoor unit in deactivation in order that a fixed circulation amount of refrigerant is retained. That is, it is necessary to prevent lack of a circulation amount of refrigerant.
Further, when one of the outdoor units is deactivated during heating operation, a large amount of gas refrigerant can be condensed in the outdoor unit or the refrigerant piping. Therefore, it is required to prevent the compressor from compressing a liquid refrigerant during a reactivation of the outdoor unit.
Furthermore, when the air conditioner has a plurality of outdoor units, the refrigerant piping extending from the outdoor units is connected to two main pipes and the main pipes are connected on the indoor side. However, in case that the piping arrangement is done by hand during installation, an angle of tilt of piping required for backing oil cannot be secured or a pan of piping to be horizontally arranged may be inclined. This disadvantageously prevents highly-reliable air conditioning.
In view of the foregoing problems, this invention has been made. The object of the present invention is to prevent the compression of liquid refrigerant and the lack of refrigerant needed for circulation resulting from the storage of the refrigerant and the like and to provide accurate installation of the refrigerant piping.